Method for pre-shaping sheet metal, and computer program and device for carrying out the method

ABSTRACT

The disclosure relates to a method for pre-shaping sheet metal (1) in strip- or panel-form having a flat cross-sectional profile into a circular arc-shaped cross-sectional profile, in a pre-shaping section (3) of a plant for producing open-seam pipes. The circular arc-shaped cross-sectional profile is provided to the sheet metal (1) in the pre-shaping section (3) by means of roll profiling in a plurality of successive bending steps in a transport direction. The cross-sectional profile is created by step-by-step bending of individual circular arc portions (8) from an outer edge of the sheet metal (1) toward a center line (7) such that the individual circular arc portions (8) directly adjoin one another or at least partially overlap. The disclosure further relates to a device for carrying out the method.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage application, filed under 35 U.S.C. § 371, of International Patent Application PCT/EP2021/080966, filed on Nov. 8, 2021, which claims the benefit of German Patent Application DE 10 2020 215 091.5, filed on Dec. 1, 2020.

TECHNICAL FIELD

The disclosure relates to a method for pre-shaping sheet metal in strip form or panel form having a flat cross-sectional profile into a circular arc-shaped or approximately circular arc-shaped cross-sectional profile, in a pre-shaping section of a plant for producing open-seam pipes. The disclosure further relates to a computer program for carrying out certain method steps of the method. Finally, the disclosure relates to a device for carrying out the method.

BACKGROUND

In the prior art, various methods are known for the production of metal pipes. Metal pipes can be produced both seamlessly and with longitudinal welds or helical welds. The latter are generally referred to as spiral pipes. Longitudinally welded pipes are made from metal strips or sheet metal formed into open-seam pipes, which are welded along a slot extending in the longitudinal direction of the bent sheet metal. The starting material is, for example, metal strips, which are unwound from coils and continuously bent into an open-seam pipe and welded together in the region of the resulting slot extending in the longitudinal direction. Alternatively, individual panels, which are processed accordingly, can serve as the starting material. In a first stage of production to form a metal pipe, the sheet metal is initially bent into a concave shape by means of various rolling mill stands in a pre-shaping section and formed into an open-seam pipe in fin-pass stands, for example in the form of knife-disk stands, and then welded and, if necessary, cut to length to form individual pipe sections.

The pre-shaping section usually comprises individual rolling mill stands with concave bottom rolls, known as break-down stands, and/or rolling mill stands with ruler guides. The rolls of the individual stands must be elaborately designed and adjusted for the respective product in order to produce a corresponding pipe. Such stands usually comprise a variety of different rolls with different radii and different dimensions. For deformation with rulers, complex design and adjustment calculations must be performed.

As an alternative to the pre-shaping of sheet metal for the production of open-seam pipes or longitudinally welded pipes, as the case may be, it is known to perform the pre-shaping with tools mounted on a circulating chain hoist. A method and a device for bending sheet metal into a so-called “molding flower” by means of forming tools mounted on an endlessly circulating chain hoist is known, for example, from EP 2 636 463 A1.

DE 699 26 406 T2 describes a method and a device for roll forming steel pipes, with which a metal strip is bent around a pinch edge at the edge side, wherein a target deformation zone of the strip is bent around a roller surface of an upper roller. Thereby, it is provided that a contact roller presses a center region of the material in the transverse direction from a bending outer side, in order to bend a W-shaped cross-section. To create the desired molding flower for inserting the metal strip into the subsequently provided fin-pass stands, stands with lateral auxiliary rollers are provided, which bend the lateral edges of the metal strip in the direction of the center line of the pre-shaping section.

SUMMARY

Known methods and devices for pre-shaping sheet metal in strip form or panel form having a flat cross-sectional profile into a circular arc-shaped or approximately circular arc-shaped cross-sectional profile have the disadvantage that either a large number of different rolls with different radii and different angles of attack or complex tools are required.

The disclosure is based on the object of providing a method for the pre-shaping of sheet metal in a pre-shaping section along with a device for the pre-shaping of sheet metal, which makes do with a reduced number of different rolls with a relatively low roll weight. The disclosure is also based on the object of automating individual steps of the method with the aid of a computer.

The object underlying the invention is achieved by a method, a computer program for carrying out at least one of the method steps and by a device that is preferably suitable and intended for carrying out the method as disclosed herein.

Advantageous embodiments of the invention are claimed.

One aspect of the disclosure relates to a method for pre-shaping sheet metal in strip form or panel form having a flat cross-sectional profile into a circular arc-shaped cross-sectional profile in a pre-shaping section of a plant for producing open-seam pipes, wherein the circular arc-shaped cross-sectional profile is provided to the sheet metal in the pre-shaping section by means of roll profiling in a plurality of successive bending steps in a transport direction, wherein the cross-sectional profile is created by step-by-step bending of individual circular arc portions or individual profile sequences, as the case may be, in each case from an outer edge of the sheet metal toward a center line such that the individual circular arc portions directly adjoin one another or at least partially overlap.

The essence of the method is that the desired radius of the pre-shaped sheet metal, that is, the target radius of the sheet metal, is gradually formed into the sheet metal from the outside inwards, such that this receives a cross-sectional contour with a continuous radius or a continuous radius profile that is not interrupted by straight sections. Preferably, a constant equal bending radius is generated from bending step to bending step. However, it can also be provided that continuously merging or overlapping profile sections, as the case may be, with different radii are generated. The method has the particular advantage that the same constant angular range from the outside to the inside can be formed from step to step, such that, if the circular arc-shaped cross-sectional profile is generated by means of a plurality of rolls in a plurality of rolling mill stands arranged one behind the other, identical top rolls and bottom rolls with a fixed angular setting or with fixed setting angles, as the case may be, may be used. This significantly reduces the number of rolls with different radii required.

With a preferred variant of the method, the individual circular arc portions are generated symmetrically in the direction of the center line, starting from both outer edges extending in the transport direction of the sheet metal.

Preferably, the circular arc-shaped cross-sectional profile is generated in a continuous pass of the sheet metal through rolling mill stands arranged one behind the other in the pre-shaping section. The sheet metal can be fed to the process both endlessly and continuously in the form of strips and discontinuously in the form of individual panels.

For example, the sheet metal can be unwound from coils and welded into a continuous strip. In a method step preceding pre-shaping, the sheet metal can be pre-bent at both edges or longitudinally extending outer edges, as the case may be, with a smaller radius by means of a bending stand. Such smaller radius can correspond, for example, to the target radius for deformation of the sheet metal to the finished open-seam pipe in fin-pass stands.

Preferably, the individual circular arc portions or profile sequences, as the case may be, are generated with the same bending radius. The bending radius of the circular arc portions can be selected to be greater than or equal to a desired target radius of the sheet metal.

With a particularly preferred variant of the method, it is provided that the bending radius with respect to a desired target radius is determined with a software-supported springback calculation, preferably based on the diameter, wall thickness and yield strength of the sheet metal and taking into account a minimum gap between the rolls, which arises from the roll width.

Preferably, the sheet metal is subjected to three-point deformation at each bending step from each outer edge symmetrical to the center line. Such a three-point deformation can be achieved, for example, by using a roll configuration with which a bending radius is generated on the inside of the circular arc portion to be formed with one support and on the outside of the circular arc portion to be formed with two supports. This can be done, for example, on each side of the metal strip with one top roll and two bottom rolls.

With a further expedient and preferred variant of the method, it is provided that at least one radius and/or one angle of attack of at least one roll and/or at least one roll configuration with respect to a desired target radius is calculated with the aid of a computer as a function of a springback calculation and taking into account the height and/or width of the roll gap. On the basis of the radius thus determined, the theoretical ideal radius for the rolls to be used in the method is obtained.

Since rolls are usually provided or kept in discrete diameter gradations, it can be provided that at least one roll is selected from a list with a plurality of rolls having different radii in a given gradation as a function of the result of the calculation by means of a computer program.

The disclosure proposes a corresponding computer program that uses appropriate algorithms to determine the roll configuration of successive bending steps based on maximum allowable edge elongations at the edges of the sheet metal. For example, the computer program can iteratively determine the required number of calibers and caliber geometry, or the required number of bending steps, as the case may be, with the associated roll configurations, in order to obtain the desired molding flower or the ideal cross-sectional profile of the sheet metal required for entry into the fin-pass stands with as few bending steps and as few rolls as possible. The term “roll configuration” within the meaning of the present disclosure is understood to mean the geometrical roll design of a rolling mill stand. The computer software can comprise at least one self-learning algorithm to determine the optimal roll configuration. This can be done by taking into account values from an FEM (finite element method) analysis of the sheet metal. For example, it is possible to specify certain limit values or boundary conditions for the deformation of the rolled material from an FEM analysis. With the method, it can be provided, for example, to determine the maximum permissible edge elongation of the strips or panels by means of FEM analysis and to transfer this as a limit value to the algorithm, thus ensuring that the strip edges do not curl.

The object underlying the invention is further achieved by providing a device for pre-shaping sheet metal in strip form or panel form having a flat cross-sectional profile into a circular arc-shaped cross-sectional profile in a plant for producing open-seam pipes. The device is preferably intended and suitable for carrying out the method with one or more of the features described above. According to one aspect, the device comprises a plurality of rolling mill stands arranged one behind the other in a pre-shaping section, each with a roll configuration that is designed in such a manner that a bending radius is provided to the sheet metal starting from each outer edge, preferably symmetrically with respect to a center line of the pre-shaping section, in a plurality of profile sequences. The center line of the pre-shaping section should ideally correspond to the center line of the sheet metal.

The device for pre-shaping sheet metal can comprise a bending stand.

Preferably, at least one rolling mill stand is designed in such a manner that the sheet metal is bent with one support on the inside of a circular arc portion to be formed and with two supports on the outside of the circular arc portion to be formed.

The rolls of rolling mill stands arranged one behind the other are expediently arranged differently. These can further have the same or different radii and/or different roll profiles.

The fact that, with an advantageous variant of the method, the profile sequences formed into the sheet metal from the outer sides in the direction of the center line have the same bending radius does not necessarily mean that the rolls in rolling mill stands arranged one behind the other must have the same radius.

At least one rolling mill stand can have a top roll, a bottom roll and a bending roll on both sides of the center line, each forming a three-point support.

Alternatively, a rolling mill stand suitable for carrying out the method can comprise a top roll and a bending roll on both sides of the center line and a single bottom roll extending on both sides of the center line.

In another embodiment of at least one rolling mill stand, it can be provided that a top roll and a bottom roll are provided on both sides of the center line, wherein the bottom roll has a roll profile that forms two supports.

Rolling mill stands with different roll configurations of the type described above can be combined in a pre-shaping section.

It is expedient to adjust the distance and/or the angle of attack of the rolls of at least one rolling mill stand with respect to the center line.

With an advantageous embodiment of the device, it can be provided that all rolling mill stands arranged one behind the other comprise the same configuration with different distances and/or angles of attack of the rolls.

An exemplary embodiments shown in the attached drawings an explained below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a systematic illustration of the forming of sheet metal into an open-seam pipe in a pipe welding plant with a pre-shaping section.

FIG. 2 is a schematic illustration of a rolling mill stand for carrying out roll profiling.

FIG. 3 is a corresponding illustration of a second variant of a rolling mill stand for carrying out roll profiling.

FIG. 4 is an illustration of a third variant of a rolling mill stand for carrying out roll profiling.

FIG. 5 is a schematic illustration of a fourth variant of such a rolling mill stand.

FIG. 6 is a schematic illustration of various successive bending steps.

FIG. 7 is a schematic illustration of different deformation states of the sheet metal in the form of a so-called “pre-shaping flower” of the sheet metal.

FIG. 8 is a schematic illustration of a device for molding sheet metal with a plurality of rolling mill stands having a roll configuration that corresponds to the variant of the rolling mill stand shown in FIG. 5 .

DETAILED DESCRIPTION

The illustration in accordance with FIG. 1 shows the individual method stages in the forming of sheet metal 1 in a pipe welding plant. Starting from a flat initial cross-section, the sheet metal 1 is provided either in the form of panels or in the form of strips, which are unwound from a coil. In a strip edge bending stand 2, the sheet metal 1 is initially bent at the edges. The sheet metal 1 is then pre-shaped in a pre-shaping section 3, which comprises a plurality of rolling mill stands 5 or pre-bending stands, as the case may be. In the pre-shaping section 3, roll profiling of the sheet metal 1 takes place in a plurality of successive bending steps to form an almost closed, circular arc-shaped cross-section. In a subsequent method stage, the pre-bent sheet metal is formed into an open-seam pipe 4 in fin-pass stands, which are designed, for example, as knife-disk stands. Finally, in a further method stage, the open-seam pipe 4 is welded along the slot extending in the longitudinal direction. The method substantially relates to the pre-shaping of the sheet metal 1 in the pre-shaping section 3.

The pre-shaping section 3 comprises a plurality of rolling mill stands 5 arranged one behind the other, in which a circular arc-shaped cross-sectional profile is provided to the sheet metal 1 by roll forming in a plurality of successive bending steps in a transport direction, wherein the cross-sectional profile is generated by gradual bending of individual circular arc portions 8 or profile segments, as the case may be, in each case from an outer edge 6 to a center line 7 of the sheet metal symmetrically with respect to the center line 7 of the sheet metal 1. This procedure is best illustrated by the sequence of bending steps a) to e) shown in FIG. 6 . For reasons of simplification, the bending steps a) to e) are shown both in the sequence in accordance with FIG. 6 and in the illustration in accordance with FIG. 3 only in relation to one side of the sheet metal 1 from an outer edge 6 to the center line 7. The bending process is carried out mirror-symmetrically on the side of the sheet metal 1 (not shown) correspondingly and simultaneously. The illustration in accordance with FIG. 6 shows the complete process of pre-bending in the pre-shaping section 3 in five rolling mill stands 5 arranged following one another in the transport direction of the sheet metal in the pre-shaping section 3 to a desired, almost closed circular arc-shaped profile cross-section, which has a desired target radius with which the sheet metal is formed into the finished open-seam pipe. The number of individual bending steps is not critical to the method, but the method is carried out in such a manner as to minimize the number of bending steps and the rolls required for this purpose. The last bending stage or the last bending step, as the case may be, is shown in image e) in FIG. 6 . As can be clearly seen from FIG. 6 , individual profile sequences or circular arc portions 8, as the case may be, are generated successively from the outer edge 6 of the sheet metal 1 in the direction of the center line 7, in a manner overlapping one another, such that a substantially continuous circular arc with a preferably constant radius is generated.

In the exemplary embodiment described in FIG. 6 , the individual circular arc portions 8 are generated, for example, by a top roll 9, a bottom roll 10 and a bending roll 11, each on one side of the sheet metal 1. The top rolls 9, the bottom roll 10 and the bending roll 11 are arranged relative to one another, such that they form a three-point support. With such a roll configuration of the rolling mill stand 5 used, a total of two top rolls 9, two bottom rolls 10 and two bending rolls 11 are provided, which are arranged, for example, in accordance with the illustration in FIG. 2 and each extend only over a partial width of the sheet metal. The top rolls 9 are each arranged on the inside of the circular arc portion 8 to be bent, whereas the bottom rolls 10 and the bending rolls 11 are each arranged on the outer side of the circular arc portion 8 to be bent. The top rolls 9 are mounted so that they can be displaced horizontally relative to one another and vertically in a rolling mill stand (not shown). The profile of the roll barrel and the radius of the top rolls 9 along with the barrel profile of the bending rolls 11 and their radius substantially define the bending radius of the circular arc portion 8 to be formed. The distance of an arrangement of top roll 9, bottom roll 10 and bending roll 11 on one side of the center line 7 from an arrangement of top roll 9, bottom roll 10 and bending roll 11 on an opposite side of the center line 7 defines the location of the respective circular arc portion 8 to be formed with respect to the center line 7.

With a variant of the method, it can be provided that the sequence of bending steps a) to e) shown in FIG. 6 , which correspond to the deformation states A) to E) of the sheet metal 1 shown in FIG. 7 , is bent with a corresponding number of rolling mill stands 5 arranged one behind the other with an identical roll configuration, which can correspond, for example, to the roll configuration in accordance with FIG. 2 , wherein the distance of the arrangement provided in each case on both sides of the center line 7, comprising in each case a top roll 9, a bottom roll 10 and a bending roll 11, varies from one rolling mill stand 5 to the next rolling mill stand 5 until, with the last bending step, an almost closed circular arc-shaped cross-section of the sheet metal is bent.

The example of a roll configuration shown in FIG. 3 on a rolling mill stand 5 for use in the method comprises, instead of two bottom rolls 10, a single bottom roll 10 extending over a substantial portion of the width of the rolling mill stand 5 and supporting the non-bent region of the sheet metal 1.

A rolling mill stand 5 with a different roll configuration is shown in FIG. 4 . The roll configuration shown in FIG. 4 corresponds approximately to that shown in FIG. 2 , wherein the bending roll 11 has a roll contour that corresponds to that of a conventional bottom roll 10 and the bending radius is influenced by the angle of attack of the axis of rotation of the bending roll 11.

Another possible roll configuration is shown in FIG. 4 . With such roll configuration, a three-point support is realized in each case with a top roll 9 and a combined bending and bottom roll 12, which is designed as a diablo roll with two frustoconical shell surfaces arranged with the conical tip relative to one another. The roll barrel of the combined bending and bottom roll 12 forms two supports, such that a three-point support with a total of two rolls can be realized. With such a roll configuration, a pre-shaping section 3 can be realized with rolling mill stands 5, each of which has only 4 relatively narrow rolls.

Depending on the size of the contact area between the individual rolls, it may be necessary to provide drivers between the rolling mill stands to transport the sheet metal 1. In principle, individual rolls of the rolling mill stands 5 can also be driven.

FIG. 8 shows a perspective and schematic view of a pre-shaping section 3 using rolling mill stands 5, which have a roll configuration in accordance with the exemplary embodiment shown in FIG. 4 . In the pre-shaping section 3, a top roll 9 and a combined bending and bottom roll 12 are arranged as a pair of rolls in rolling mill stands 5 following one another on both sides of a center line 7, wherein the distance between the pairs of rolls provided on both sides of the center line 7 decreases gradually from one rolling mill stand 5 to the next rolling mill stand 5 from an inlet side of the sheet metal 1 to an outlet side of the sheet metal 1.

LIST OF REFERENCE SIGNS

-   -   1 Sheet metal     -   2 Bending stand     -   3 Pre-shaping section     -   4 Open-seam pipe     -   5 Rolling mill stands     -   6 Outer edge of the sheet metal     -   7 Center line of the sheet metal and center line of the         pre-shaping section     -   8 Circular arc portions     -   9 Top roll     -   10 Bottom roll     -   11 Bending roll     -   12 Combined bending and bottom roll 

1.-19. (canceled)
 20. A method for pre-shaping sheet metal (1) in strip form or panel form having a flat cross-sectional profile into a circular arc-shaped or approximately circular arc-shaped cross-sectional profile in a pre-shaping section (3) of a plant for producing open-seam pipes, the method comprising: roll profiling the sheet metal (1) in the pre-shaping section (3), in a plurality of bending steps following one another in a transport direction, to provide the circular arc-shaped or approximately circular arc-shaped cross-sectional profile, wherein the circular arc-shaped or approximately circular arc-shaped cross-sectional profile is created by step-by-step bending of individual circular arc portions (8) from an outer edge of the sheet metal (1) toward a center line (7) such that the individual circular arc portions (8) directly adjoin one another or at least partially overlap.
 21. The method according to claim 20, wherein the individual circular arc portions (8) are generated symmetrically toward the center line (7), starting from both outer edges (6) extending in the transport direction of the sheet metal (1).
 22. The method according to claim 20, wherein the circular arc-shaped cross-sectional profile is generated by a plurality of rolls in a plurality of rolling mill stands (5) arranged one behind the other.
 23. The method according to claim 20, wherein the circular arc-shaped cross-sectional profile is generated in a continuous pass of the sheet metal (1) through rolling mill stands (5) arranged one behind the other in the pre-shaping section (3).
 24. The method according to claim 20, wherein the circular arc portions (8) have the same bending radius.
 25. The method according to claim 20, wherein a bending radius of the circular arc portions (8) is selected to be greater than or equal to a desired target radius of the sheet metal (1).
 26. The method according to claim 20, wherein a bending radius with respect to a desired target radius is determined using a software-supported springback calculation.
 27. The method according to claim 20, wherein the sheet metal (1) is subjected to three-point deformation at each bending step from each outer edge (6) symmetrical to the center line.
 28. The method according to claim 27, wherein the three-point deformation is generated with a roll configuration with which a bending radius is generated on an inside of the circular arc portion (8) to be formed with one support and on an outside of the circular arc portion (8) to be formed with two supports.
 29. The method according to claim 25, wherein at least one radius and/or one angle of attack of at least one roll and/or at least one roll configuration with respect to a desired target radius is calculated by a computer as a function of a springback calculation and taking into account a height and/or width of a roll gap.
 30. The method according to claim 29, wherein at least one roll is selected from a list with a plurality of rolls having different radii in a given gradation as a function of a result of the calculation by a computer program.
 31. A computer program comprising instructions that, when the program is executed by a computer, cause the computer to execute the method according to claim
 29. 32. A device for pre-shaping sheet metal (1) in strip form or panel form having a flat cross-sectional profile into a circular arc-shaped cross-sectional profile in a plant for producing open-seam pipes, comprising: a plurality of rolling mill stands (5) arranged one behind the other with respect to a pre-shaping section (3), in each case with a roll configuration that is designed in such a manner that a bending radius is provided to the sheet metal (1) in a plurality of profile sequences starting from each outer edge (6), symmetrically with respect to a center line (7) of the pre-shaping section (6).
 33. The device according to claim 32, wherein the rolls of at least one rolling mill stand (5) are designed in such a manner that the sheet metal (1) is bent with one support on an inside of a circular arc portion (8) to be formed and with two supports on an outside of the circular arc portion (8) to be formed.
 34. The device according to claim 32, wherein the rolls of rolling mill stands (5) arranged one behind the other are arranged differently and/or have different radii and/or different roll profiles.
 35. The device according to claim 32, wherein at least one rolling mill stand (5) has at least one top roll (9), one bottom roll (10) and one bending roll (11) on both sides of the center line (7), each forming a three-point support.
 36. The device according to claim 32, wherein at least one rolling mill stand (5) comprises at least one top roll (9) and one bending roll (10) on both sides of the center line (7) and a single bottom roll (10) extending on both sides of the center line.
 37. The device according to claim 32, wherein at least one rolling mill stand (5) comprises at least one top roll (9) and one bottom roll (12) on both sides of the center line (7), wherein the bottom roll has a roll profile that forms two supports.
 38. The device according to claim 32, wherein a distance and/or an angle of attack of the rolls is adjustable with respect to the center line (7). 